Motor controllers control motors in general, and, in particular, control the torque outputs of motors by regulating the current. Motor controllers utilizing current control loops in controlling motors are well known in the art. The current control loop may be placed inside of a speed or position control loop. The control loops requires, as an input, the rotational motor position. Typically, the current is controlled to be in alignment with the rotational motor position. One way of determining motor position is by using a sensorless motor control approach. The sensorless motor control approach does not use a sensor to sense the position of the motor but instead typically uses an observer. The observer is herein defined as an operational block, device, or system that determines the motor position as a function of the electrical input/output (“I/O”) of the motor. They have been developed to avoid at least some of the issues that sensors typically add. The electrical I/O is typically the voltages and currents present at the terminals of the motor.
FIG. 1 shows a conventional sensorless, field-oriented control (FOC) motor control system 100 in accordance with the prior art. Motor control system 100 generally includes a motor controller 102, a power supply 120, an inverter 122, a motor 124, and a current observer 126. The motor 124 is typically a permanent magnet synchronous motor (PMSM) or brushless direct current (BLDG) motor. Typically, the motor has three terminals, although other configurations are also used. The motor controller 102 generally comprises a proportionate-integral (“PI”) controller 103, an inverse Park converter 108, an inverse Clarke converter 110, a three phase (3-Ø) pulse width modulation (PWM) controller block 112, and a rotor position observer 118. The inverse Park converter 108 performs inverse Park transformations on the outputs from the PI controller 103, rotating the control feedback vector from a rotor centric platform to a stator centric value. The inverse Clarke converter 110 performs inverse Clarke transformations on the two outputs from inverse Park converter 108 to transform them from a two-dimensional signal into three output signals. The three output signals from the inverse Clarke converter 110 are provided to PWM controller block 112. The PWM controller, by varying the pulse width, provides a voltage in conformity with its input signal without the power loss of a linear regulator. The outputs from PWM controller block 112 are provided to inverter 122. The motor controller 102 further includes a Clarke converter 114 for respectively receiving three signals from motor 124 via current observer 126 and performing Clarke transformations thereon. The Clarke converter 114 converts the three input signals from motor 124 to two output signals, representing the current signal in the stator frame of reference. The two output signals from the Clarke converter 114 are fed into a Park converter 116 for performing Park transformations which are mathematically equivalent to complex rotations, transforming the current value to the frame of reference of the rotor. Park converter 116 provides outputs to respective proportionate-integral (“PI”) Q controller 104 and proportionate-integral (“PI”) D controller 106. PI Q controller 104 and PI D controller 106 can be viewed or considered together as a PI controller in the complex domain. PI Q controller 104 provides and handles the “Q” integral aspects of the PI controller while PI D controller 106 provides and handles the “D” integral aspects of the PI controller. The input target current Itarget to the control loop is the desired current.
During operation, the PWM controller block 112 of motor controller 102 provides continuous PWM signals to control inverter 122 so that inverter 122 can provide commanded voltage to each phase of motor 124 from power supply 120. Motor controller 102 provides control of motor 124 through the application of PWM signals from PWM controller block 112. Rotor position observer 118 determines the rotor position or angle and provides an angle signal, used as a rotation value, to the Park converter 116 and inverse Park converter 108.
Motor control systems and methods that use motor control loops are well known in the art. Such an exemplary prior art conventional motor control system and method are disclosed in U.S. Patent Application Publication No. US2012/0249033 to inventor Ling Qin entitled “Sensorless Motor Control” (hereafter referred to as '033 patent application). Paragraph 0005 of the '033 patent application further cites exemplary conventional motor control systems and methods in accordance with the prior art. Also, another prior art conventional motor control system and method are disclosed in the Texas Instruments' (TI) white paper entitled “Designing High-Performance and Power-Efficient Motor Control Systems” by Brett Novak and Bilal Akin dated June 2009. Such motor control systems and methods suffer from deficiencies.
For example, the current control in such motor control systems and methods that use motor control loops is less accurate than desired, largely due to the bandwidth limitations of the control loop. Thus, the current control accuracy and/or speed are often set by the delay in the feedback loop. Any outer control loops, such as the loops needed for speed or position, must similarly be decreased in bandwidth to provide phase margin. Referring to FIG. 1, system 100 shows PI Q controller 104 and PI D controller 106 receiving the input target current Itarget. The outputs from PI Q controller 104 and PI D controller 106 are provided to inverse Park converter 108. PI Q controller 104 sets the desired current magnitude for controlling motor 124 while PI D controller 106 sets and provides a zero level reference. The Clarke and inverse Clarke converters 114 and 110 perform the transformations that handle the conversion from a winding of motor 124 to rectangular or complex coordinates. The Park and inverse Park converters 116 and 108 handle rotating the frame of reference for the PI control loops. Clarke and inverse Clarke converters and Park and inverse Park converters are well known in the art.
System 100 requires significant computation and adds feedback delay. A number of variants of the control topology of system 100 exist and are well known in the motor control art. A motor control system and method that requires a low or lower amount of computation requirements and has faster feedback control (e.g., low, lower, or minimal feedback delays) are desired.